I never had the chance to interact with @marcus since I have no background of many of his areas of expertise. But seeing his profile, content and feelings of members in this thread, I can see he had a vast scientific knowledge. He was surely one of the best science advisors here on PF! I now wish I had a little knowledge of any of those topics and I could interact with him. It would have been a great experience! My condolences to his family! Rest in peace marcus!

My condolences. I interacted with him a couple of times. He was a frequent poster in the Cosmology and Beyond the Standard Model forum, and he was always friendly and very interested in many things. I am sad by the news .

I have since long known that if I decided to cling actively on a forum like PF comprising people of all ages, on a certain day I will get notified about the resignation of a certain member. Just, I never have thought that this time's notification of leave, that came less than two years since I joined in PF, is about an unwakeable rest.
For a theory that bears the potential of revolutionizing physics, Marcus's retirement is a big loss.
Deep condolences for the deceased's family and relatives.

Condolences to you and family.
We know that he will be severely missed your family, but also on this and quite a few other science forums.
Without your dad's inspiration and support, the community-development of the LightCone cosmological calculator would probably not have happened.

My condolences, Marcus was always able to supply excellent counter points to LCDM in LQC based models. I always enjoyed his counter points to numerous threads where I've supplied one variation to an answer, then he supplied another.

I also enjoyed working with him on the lightcone tutorial development. He had a natural way to extend the flexibility of the calculator well beyond its first appearance.
His true gift was simplifying the complex mathematics for numerous posters who didn't have strong math skills.

What sad news. My deepest condolences go out to Marcus's family, friends and everyone whose lives he touched. I'm deeply indebted to him for his patience and knowledge which have helped me to understand some of the complexities of our wonderful Universe.

I know of little else that impacts humans as deeply as death because we all seem so helpless in the facing of it. I am very grateful that you, tamwuff, saw fit to let us know some details during your time of grief. I find that a bit heroic and also somewhat understandable given the influence of a good man like Marcus. Please accept my deeply sincere expression of love and respect for your father for all his drive to share his knowledge so unselfishly. Also trust that once the physical process of grief has has diminished, while you will forever miss him as so many of us here will, you, like us, will find that grief ultimately greatly outpaced by the goodness and brightness of the man and the manner of life he apparently led. This thread is certainly testament to a major aspect of that. Peace to you and yours.

This is very sad, and a stark reminder of our own transience and mortality. I have not known him for long, but it is safe to say that not only did a remarkable human being pass on, but along with him also an incredible amount of knowledge and understanding on this universe we are all part of. A lifetime to accumulate, yet lost in a moment.

He is a legend, like his favourite Marcus, Marcus Varro (Varro Reatinus), the most brilliant polymath of Ancient Roman world. Augustine wrote of that Marcus, homo omnium facile acutissimus et sine ulla dubitatione doctissimus (Aug. Civ. 6,2) [5.1179], (roughly, “The most perspicacious and without doubt, easily most learned”).

Our Marcus wrote of harmony, and "Varro produced a remarkably broad spectrum of works that covered almost all areas of intellectual inquiry.... all of which were complemented by his own colourful poetic composition” (Butterfield), with understanding for diverse fields, and considering those verbal and those to do with proportion and motion, harmoniously.

@tamwuff. I would like to offer my condolences as well. I haven't had the skills to discuss topics on his level but I always knew what a great contribution he made to this community. I am saddened by the loss of one of our great ones.

My sincerest condolences to tamwuff and their family.
I've seen marcus's posts, but I have never contacted with him in the forum. Still, I shared the sorrow of his passing. I wish I had the chance to meet him.
May your soul rest in peace..

@tamwuff. I would like to offer my condolences as well. I haven't had the skills to discuss topics on his level but I always knew what a great contribution he made to this community. I am saddened by the loss of one of our great ones.